Modern integrated circuit technology offers the possibility to integrate magnetic sensors and their readout and angle determination circuit on a single die. This allows providing detectors of mechanical rotation which consist of a permanent magnet attached to a rotor and a monolithically integrated sensor attached to a stator, at competitive cost and good performance. The absence of mechanical contact between the rotor with the magnet and the stator with the sensor allows for hermetic encapsulation of the sensor. This permits wear-free angle measurements under harsh environmental conditions.
Various structures, devices and methods for measuring such a magnetic field (or field component) are known in the art. Many of them are based on so called “horizontal” or “vertical” Hall elements, which are integrated in the semiconductor devices. Horizontal Hall elements are typically implemented by forming an isolated Hall-plate (semiconductor region), substantially parallel to the plane of the semiconductor device, (hence the name “horizontal”), and are typically in the shape of a square, whereby a current is injected in one corner and drawn from the opposite corner, these corners are referred to as “biasing contacts” or “supply contacts”, while a differential voltage (so called Hall voltage) indicative for a magnetic field component Bz vertical to the plane of the sensor plate is measured over the remaining corners, referred to as “sensing contacts”, or “readout contacts” or “output contacts”. Vertical Hall sensors are primarily built in the depth direction of the silicon, and may e.g. have five contacts on the surface (although less than five is also possible), whereby a current is injected in the middle contact (e.g. by connecting it to a supply voltage VDD), which current is drawn from the outer contacts (e.g. by connecting it to a ground voltage GND), while a differential voltage indicative for a magnetic field component parallel to the semiconductor plane is measured from the remaining two contacts, referred to as “sensing contacts”, or “readout contacts” or “output contacts”. The middle and outer contacts are referred to as the “supply contacts” or “biasing contacts” of the vertical Hall sensor.
Ideally, in the presence of no magnetic field, the sensors should output zero differential voltage, also referred to as “Hall potential” or “Hall voltage”. In practice however, this is not always the case, and a small voltage signal, called offset-voltage is provided, which needs to be compensated. Known methods are e.g. the so called “contact commutation method”, also known as “spinning-current method”, whereby each electrical contact serves sequentially as supply contact and readout contact.
Another problem is related to the small differential signal generated by such Hall elements, which are typically in the order of 100 microVolts to 1 milliVolt, and thus need to be amplified before it can be used for further processing. Ideally, in the presence of no differential signal, the output of the amplifier should be exactly zero, but in practice it is not, and the offset voltage appears as a DC-offset at the output, which needs to be compensated for.
EP0916074(B1) describes a method and arrangement for contactless angle measurement using a magnetic field originating from a two-pole magnet, whereby an axial field component Bz in parallel with the rotation axis is measured by sensor elements at several spots inside a plane perpendicular to the rotation axis. By measuring two orthogonal field components Bx, By, the orientation of the magnet can be determined, using goniometric functions.
EP2153241(B1) describes a circular vertical Hall sensor. This sensor uses a circular vertical Hall structure whereby groups of contacts are sequentially scanned in clockwise or anti-clockwise direction. The offset-reduction is done via the well known contact commutation method (or spinning-current method). The angular position of the magnet is determined via the phase of the scanned signal.
Also EP2000814(B1) describes several embodiments of circular vertical Hall sensors. In particular, the embodiment of FIG. 7 uses an outer ring and an inner ring whereby current is flowing in a radial direction, and a differential signal is derived from two sensing electrodes located at opposite sides of the inner ring, at 180° angular distance. In the embodiment of FIG. 10 (replicated as FIG. 1 attached hereto), the outer ring is replaced by individual outer contacts, aligned at the same angular position as the sensing electrode located between the outer contacts and the central ring. In this figure, it is easy to recognize the “five contacts” of the vertical Hall sensor mentioned above, and indicated in black. FIG. 13 (replicated as FIG. 2 attached hereto) shows a block-schematic of a circuit for biasing and reading-out the structure of FIG. 1, and for determining the angular position of the magnetic field.